The invention relates to a method and a device for the optimized negotiation of communication parameters for the transmission of data on communication links.
A communication link is a coupling of at least two data terminals for the purpose of exchanging information. The line may be either generated for a specified time or is constantly available. The information is presented in form of a string of digital signals called bytes. The transmission of the bytes can take place in an analog or digital manner. An analog transmission, for instance, takes place in a conventional telephone network (so-called public switched telephone network (PSTN)). The analog transmission of data requires, however, a conversion of the digital signals into audio frequency signals, which are sent via the line. This is realized by means of a modulation method. The analog signals received by the receiver are demodulated and converted into digital signals. For this purpose modems are used between a data terminal equipment and the analog telephone network. Thus, the modems have the task of providing the digital signals sent by the data terminal equipment to the transmission link, which constitutes an analog transmission medium, and of adopting the received signals of the transmission link to the physical conditions of the data terminal equipment.
Another possibility of transmitting data consists in applying a digital switching technique. Said technique is, for instance, used in the widely spread ISDN (Integrated Services Digital Network) network. It is the aim of the network to obtain an integration of different telecommunication services in one universal telecommunication network. This particularly means that up to eight different or identical terminals, for example, telephone, fax, computer, videophone, can be connected to an ISDN access via a uniform interface. Another property of the network consists in the data transmission of 64 kbit/s for all services. Important standards for the data communication via ISDN are ETS 300 102-1, ITU-T I.411 and ITU-T V.110.
Another network forming part of the category of digital networks is the digital mobile communication network GSM (Global System for Mobile Communication). The usable data transmission rate is 9.6 kbit/sec per channel. When the GSM system was designed, it was particularly considered important to make services, that had previously been accessible via the conventional telephone network or ISDN, also accessible to GSM users. This refers to services such as facsimile, source data transmission or the access to data networks such as the internet. GSM offers the possibility to set up a connection to another ISDN and PSTN subscriber. In order to meet this requirement, networks of different types have to be coupled with each other. In this connection, i.e. the coupling of several networks, the term heterogeneous network is introduced and used therefor in the following.
As was already explained above, the networks differ from one another due to the transmission rate. Moreover, there is a plurality of additional parameters, which either have to be set or can be set optionally, the configuration of which, however, considerably influences the efficiency of the transmission.
For instance, in order to guarantee synchronization of data between a transmitter and a receiver, a choice has to be made between a synchronous or asynchronous transmission. In asynchronous transmission there is no common time pulse. The synchronization of the transmission is done by sending start and stop bits. Said bits enclose small amounts of data produced with the transmitter by means of fragmentation of complete messages, which are reassembled with the receiver so as to form complete messages. This, however, requires an agreement between the communicating units in view of the form of transmission. In this respect, the more efficient, i.e. the synchronous form of transmission can be applied. With the synchronous transmission an identical time pulse is required by both the transmitter and the receiver. The transmission of the pulse can take place in different ways, such as on a separate pulse line, or the clock pulse may be derived from the data stream by means of a PLL. Thus, it is however absolutely necessary to have both data terminal equipment adjusted identically. Said decision is to be made by the user, wherein it has to be taken into account that presently the synchronous type of transmission holds the status of a new service with the result that it is not already implemented by all network providers. This has, therefore, to be inquired by the user. Further important parameters, which are necessarily to be agreed upon if the GSM network is involved in the transmission, refer to the transmission mode, in particular to the so-called transparent or the so-called non-transparent mode. The essential distinguishing feature is that in addition to the standard error-correcting mechanisms an additional method for correcting faulty transmitted data as well as for the buffering of data is applied in the so-called non-transparent mode. This is of significance in case of a faulty transmission channel with which the GSM is characterized. The corresponding transmission mode is selected by the user and depends on the network. Thus, the user is also required to have knowledge in view of the configuration of connections.
The two above-discussed servicesxe2x80x94synchronous/asynchronous and transparent/non-transparentxe2x80x94only form one part out of a plurality of different services. Their number and kind varies in response to the underlying network.
For the adoption of the transmission parameters not only the underlying network, e.g. ISDN, GSM or analog: PSTN, but also the kind of the terminal used by the data terminal equipment is important. On one hand, the kind of the terminal depends on the underlying network, e.g. in analog networks a modem is applied and a terminal adapter (TA) in digital ones. On the other hand, there are differences in view of the parameters between the terminals of the same kind. The parameters may, for instance, vary on the basis of the transmission rate, e.g. 14.4 kbits/s, 28.8 kbits/s and 33.3 kbits/s.
When looking at a heterogeneous connection, at least one intermediate node is involved beside the terminals in data transmission, the task of which is to adopt the linked partial paths in view of the given network characteristics. For instance, a component called InterWorking Function (IWF) integrated in the GSM switching center (so-called mobile services switching center (MSC)) is responsible for adopting the transmission carriers between GSM and external networks. Said function converts the different modulation and signaling methods into one another. The conversion methods differ from one another due to the network connected between the InterWorking Function and the subsequent data terminal equipment. The cooperation between a mobile phone and an InterWorking Function is described in standard GSM 09.07.
It is, however, a problem that it is sometimes difficult for an InterWorking Function to make a difference as to whether the subsequent data terminal equipment is connected to a digital or an analog network. The InterWorking Function generally recognizes on the basis of the kind of switching center, to which the data terminal equipment is connected, which kind of data terminal equipment is concerned. This does not take place, however, if the subscriber is in another national network and the connection is set up via several networks, where intermediate nodes use a different kind of signaling, called National User Part Signaling. Said kind of switching node may support the transmission rate of 64 kbits/s, however, uses signaling protocols which deviate from the ISDN Standard. This can result in problems when selecting the transmission parameters through the InterWorking Function.
The data terminal equipment, which refers to both the terminals and the intermediate nodes, have the task to assure a parameter agreement such that a safe and stable data transmission between the communicating data terminal equipment is guaranteed. The parameter adjustment between the data terminal equipment takes place in the set-up phase of the connection. An example of a parameter agreement during a set-up phase of a connection is introduced in the following by means of a connection between two GSM subscribers.
For transmitting data with a mobile phone, said mobile phone has to have the possibility to connect a corresponding input and output device therewith, and it has to support the necessary protocols. The input and output device is a computer, e.g. a portable computer. The data transmission in a mobile environment can also be realized by means of a special device, into which both functions, namely of a computer and of a mobile phone, are integrated. The connection between both data terminal equipment takes place via a digital interface, e.g. a PCMCIA (Personal Computer Memory Card Industry Association) card. The function thereof together with the mobile phone corresponds in the larger sense to the function of a modem. This is seen in a larger sense only, as the PMCIA card does not perform a modulation or demodulation due to the fact that it connects two digital devices.
The controllability of said card is obtained by using AT-commands. The AT-commands describe the programming language standardized under the modems. The application of the AT-commands allows the user to set the transmission parameters, such as the setting of the modem type, the transmission rate, the type of transmission (synchronous/asynchronous). In digital networks said settings are converted into the so-called bearer capability. The concept of the bearer capability was introduced in the standardization of the ISDN network and adopted to said standard in GSM standardization. The bearer capabilities deliver information on the transmission capability of data between data terminal equipment. The description of the GSM bearer capability can be inferred from GSM 04.08 and that of the ISDN bearer capability from ETSI Q.931.
The bearer capability thus describes the telecommunication service. In case of GSM the connection parameters set by the user are translated into a bearer capability, which is sent to the mobile service switching center (MSC) as a signaling message during the connection set-up phase. The bearer capability is analyzed in the MSC, and in response to the preferences of the MSC the following cases can occur.
First case: The connection is disconnected. The user can understand this to be an indication for the incorrectly set parameters. The cause of the disconnection is transmitted to the subscriber in the form of a briefly drafted information, from which the actual cause cannot be inferred, e.g. xe2x80x9ccarrier not supportedxe2x80x9d. When this case occurs, it is expected by a user to try with a different parameter setting. Said manual settings and attempts require in any case knowledge by the user.
Second case: The MSC selects parameters other than the ones it had been sent. The newly specified parameters are transmitted to the user. A logic in the mobile phone then decides whether it can accept the parameters or whether it should disconnect.
In the third case the MSC accepts the parameter setting, whereupon stand-by to support the service desired by the user is signalized.
As a result of the acceptance of the parameters in the GSM switching center, i.e. when the third case occurs, or when, in the second case, the parameters are accepted by the mobile phone, the connection set-up process is continued by including the InterWorking Function. In response to the type of transmission, either digital or analog, the connection is switched further into an analog network such as PSTN via a modem, or into a digital network such as ISDN via an ISDN adapter. If the connection is switched via an ISDN network, a translation of the bearer capability by means of the InterWorking Function takes place at the coupling points. Due to the fact that said parameters are different from one another in the two networks in view of the different bit occupancy and the different data fields, the incorrect parameter translation or loss of information can be the result. In particular, ISDN does not support the so-called auto-baunding, which is characteristic for a modem communication. The so-called auto-baunding procedure permits a dynamic negotiation of the transmission rate and the modulation. Said procedure provided for analog data terminal equipment is, however, not supported in the pure digital ISDN network.
At the time of the parameter translation from GSM to ISDN on the side of the calling subscriber is not yet known, whether the data call will terminate in the ISDN network or goes to a switching center, as this cannot be determined on the basis of the signaling. The auto-baunding is, therefore, represented in the bearer capability field being responsible for the transmission rate by means of a special bit combination. In case there is a GSM switching center on the side of the subscriber called, the information fields of the bearer capability are retranslated. The special bit combination for auto-baunding is thereby interpreted such that the highest possible supported data rate of the calling subscriber is selected. The maximum possible data rate of the calling subscriber, however, is unknown as the bearer capability field responsible for the transmission rate is occupied with the information auto-baunding. If, moreover, the transparent transmission mode is selected, the data connection will fail if the called subscriber supports a data rate higher than that of the calling subscriber. The so-called non-transparent mode permits an intermediate storage and buffering of the data in the InterWorking Function, in case the transmission rates of the transmitting and receiving side differ from each other. If, however, the setting to the transparent mode is active, the intermediate storage of data is not permitted, and at different transmission rates this can result in a data accumulation and data loss as a consequence thereof. During the connection set-up phase this is recognized to be a problem as a result of which the connection is discontinued.
If the connection between a mobile subscriber and the corresponding InterWorking Function (IWF) is set up successfully, a parameter negotiation between the subscriber""s MSC and the target subscriber is started. The parameters are transmitted in a signaling message to the mobile-phone of the called subscriber, which can decide whether the parameters are to be accepted or modified. The possibly modified parameters are sent back to the switching center of the target subscriber, which can accept them or disconnect the connection. Thereupon, the data terminal equipment are connected and the data transmission starts.
In case of heterogeneous connections, in which case different networks and data terminal equipment are involved in the transmission of information, it is difficult due to the different parameters, which have to be known in advance and have to be configured correctly, to set up a stable and safe connection between two data terminal equipment. The incompatibility between the different networks in view of the transmission parameters frequently entails the disconnection during the connection set-up. In order to perform a successful connection set-up it is presently required to know all parameters of the network and the opposite terminal. Thus, experience in the field of connection configuration by the user is required. On the other hand, not all services are supported by all network providers. At present, for instance, the synchronous transmission type is said to be a new service, which results in that it is not implemented by all network providers. The user also has to obtain information in this respect prior to his wish to set up a connection.
In most cases where the call is disconnected during set-up, an error analysis is very difficult or impossible. This means that the user is not in a position to obtain information on the cause of the error, as the error messages sent by the network contain information only to a small extent. Upon receipt of such information the user can attempt only intuitively to set up a new connection with other parameters.
Accordingly, it is the object of the invention to provide a method and a device setting up a connection to any target device by guaranteeing an optimized transmission. It is particularly an object of the invention to set up a connection to a target device, the parameters of which are unknown, also by guaranteeing an optimized transmission.
According to the invention this object is provided by means of the teaching of patent claim 1 and the teaching of patent claim 14.
Through the analysis of the list of parameters received by the communication initializing unit, a determination of communication link bottlenecks and errors is possible. This can prove to be particularly advantageous for network providers, as they are put in the position to send more exact error information to users.
It is also advantageous that a communication link is set up via a heterogeneous network.
Another advantage is that a subsequent connection to the same target device is optimized by storing the parameter setting of the once set-up connection and by re-using it with the next connection set-up.
Another advantage is also that said protocol does not define the type and number of the parameters admitted to the negotiation. With this protocol also parameters are negotiated, which are specific for a partial connection only, e.g. only for GSM.
Another advantage is also that due to the protocol being independent of the devices involved in the transmission, an update of a device in view of software or hardware takes place without having to use the functionality of the whole system.
It is also advantageous that a user being inexperienced in the configuration of a communication link can set up a communication link to any target terminal device.
Further advantages of the invention can be inferred from the dependent claims 2 to 13.